DETROIT — A Nigerian man pleaded guilty Wednesday to attempting to bring down an international flight over Detroit with a bomb in his underwear, telling a surprised courtroom on the second day of his trial that the failed attack was retaliation for the killing of Muslims worldwide.

Umar Farouk Abdulmutallab, who had never denied the accusations against him, calmly answered questions from U.S. District Judge Nancy Edmunds before pleading guilty on the second day of his trial to all eight charges he faced, including conspiracy to commit terrorism and attempted use of a weapon of mass destruction.